Physical or pharmacological disruption of chemical signals between the systemic blood flow and the brain im- pairs normal functioning and responsiveness of the brain. Long-range chemical signaling through dysregulation of cytokines, nutrients, growth factors, hormones, lipids, neurotransmitters, drugs and their metabolites is also important, but these chemical signals are difficult to quantify and cells are usually studied n isolation. The blood-brain barrier (BBB) dynamically controls exchange between the brain and body, but this cannot be studied directly in the intact human brain or adequately represented by animal models. Most existing in vitro BBB models do not include neurons and glia with other BBB elements and cannot adequately predict drug efficacy and toxicity. This research will develop an in vitro, three-dimensional, multi-compartment, organotypic model of a central nervous system (CNS) neurovascular unit (NVU) and cerebral spinal fluid (CSF) compartment, both coupled to a realistic blood-surrogate supply system that also incorporates circulating immune cells. Primary and stem-cell-derived human cells will interact with a variety of agents to produce critical chemical communications across the BBB and between brain regions, providing a compact device that faithfully reproduces the properties of the human BBB, the CNS, and the CSF. The proposed in vitro BBB/CNS/CSF model will have a small volume, requires a limited number of human cells, can recreate interactions between different brain regions, and will be coupled in real time to advanced electrochemical and mass spectrometry instruments. This transformative technological platform will replicate chemical communication, molecular trafficking, and inflammation in the brain, and will enable targeted and clinically relevant nutritional and pharmacologic interventions or prevention. This platform will be used to examine the role of the BBB in modulating chemical body-brain interactions, characterize glial and neural cell interactions in the brain, and assess the effect of a wide range of drugs, chemicals, infectious agents and xenobiotics on various brain regions. The model's clinical utility rests on its ability to 1) recreate unique regions by selecting specific combinations of neurons, endothelial cells, astrocytes, other neuroglia, pericytes and systemic leukocytes, 2) use cells and fluids derived from patients with known pathologies to assess drug treatments and physiological stress from chronic diseases such as obesity and acute injury such as stroke, 3) uncover potential adverse effects during drug discovery as well as those that are being used in clinical trials, such as toxic transformation of approved drugs by brain endothelial cells, 4) detet novel and unbiased correlations between large numbers of chemical signals which converge at the BBB, and 5) combine microfluidic devices, state-of-the-art cell culture and organotypic human brain-cell preparations, analytical instruments, bioinformatics, control theory, and neuroscience drug discovery. An integrated approach will provide technologies of widespread applicability and reveal new mechanistic and region-specific insights into how the brain receives, modifies, and is affected by drugs, neurotropic agents and disease.